Our project analyzing the spatial and temporal context in the relationship between discharge (cfs) and turbidity (fbu) in the Elwha River below the Glines Canyon Dam removal site highlighted some key trends in sediment transport post-dam removal. Our findings of a statistically significant positive correlation between discharge and turbidity suggested, as one would likely expect, that higher streamflows increase the suspended sediments in the Elwha River. This response is common in streams and well understood, but a good baseline to draw when a large and historic event has mobilized such vast amounts of sediments from the reservoir above this stream. Additionally, in looking at our median turbidity plot (Figure 4) as well as the decomposition plot (Figure 6), we can find a stabilizing trend in the transport of suspended sediments downstream as time passes since the dam was removed. This finding contributes to and aligns with general sediment transport theory and what would be expected post-dam removal.
Despite our results’ significance and alignment with basic expectations of the river system’s response to this historic event, our study does have limitations. Our scope of spatial analyses is quite small, restricted to just the two USGS monitoring stations, which limits our ability to assess the spatial effects of this event across the whole downstream section of this river below the dam and all the way to the Strait of Juan de Fuca in Washington State. Additionally, our dataset is limited to only a post-removal period, without the ability to understand the streamflow dynamics and historic sediment flows with the reservoir and dam in place. Further, our analyses did not investigate any changes in the relationship between discharge and turbidity across time or space.
Further research and investigations should include insight into local spatial trends, as well as some form of hindcasting in order to better understand how this system might have looked prior to removal and how this historic event changed the hydrologic and geomorphic regime of the Elwha River. Finally, investigations into changes in the relationship between discharge and turbidity, either spatially or temporally, could also assist in the understanding of how this dam removal altered this critical physical water relationship.
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